1. Field of the Invention
The present invention relates to computer networks and to interface devices for connecting host computers to networks. More particularly, the present invention relates to alert messages sent for system management support by network interface cards in network connected systems.
2. Description of Related Art
Computer systems include network interfaces that support high speed data transfer between the host computer and the data network. Often, such computer systems include system management resources to monitor system and power management events, and generate alert signals upon certain types of events. The alert signals are used by management logic in the system in a wide variety of ways, to improve reliability and performance of the system.
Many computer systems include power management logic which puts the system to sleep, or in a low power mode, in response to activity in the system. When the system is asleep, for example, the operating system (OS) ceases operation. To bring the system awake, the operating system must be reloaded, such as through a boot sequence. When the operating system is inactive, the power consumed by the system is reduced. Such systems can be said to have an OS-present state, and an OS-absent state. Protocols have been developed by which remote management systems can wake up a system in an OS-absent state, by sending special wake up packets which the network interface is adapted to recognize without host assistance.
Increasingly, remote management systems are used which communicate over data networks. When alerts occur, network packets are produced and forwarded to the remote management station. In the prior art, packet transmission in support of system and power management systems has been conducted under the control of the operating system. Thus, in a sleep mode, or other OS-absent mode, the remote management systems have not been able to receive timely notifications of alert conditions.
These network interfaces are typically based on a first-in-first-out (FIFO) buffer. Thus, packets coming onto the network interface, either from the network or from the host computer are stored in the FIFO. The first packet into the FIFO is transmitted out first in order to maintain sequential data transfers. The FIFO structure is an efficient, high throughput system for managing high speed network interfaces such as Gigabit Ethernet interfaces.
One prior art network interface, has been constructed so that in an OS-absent mode, the network interface is able to transmit keep alive messages to remote management systems on the network. The keep alive messages are loaded into the FIFO buffer of the network interface chip in connection with a transition to an OS-absent state. Logic in the network interface chip remains operational during this state to transmit the keep alive messages. The keep alive messages may be configured in this prior art device to be transmitted periodically in response to an interval timer, and in response to wake up packets from a remote management station. The keep alive messages may also be configured to be transmitted only when a control code in a packet header matches a signal received on one of the I/O pins on the network interface chip. This allows a system configuration where an external event, such as fan speed, over-temperature, or over-voltage can cause assertion of an event signal on one of these pins, and cause transmission of an alert packet on the network.
Alerts in connection with system and power management events are diverse. The approach of the prior art network interface is relatively inflexible, and difficult to integrate with standard systems, such as the SMBus, used for monitoring and communicating signals about system and power management events. (See, System Management Bus (SMBus) Specification, Version 2.0, SBS Implementers Forum, Aug. 3, 2000.) It is desirable therefore, to provide for more flexible and efficient system for alert packet transmission, operable during an OS-absent mode.